On paper, the diesel Stelvio and petrol Macan make an interesting pairing. Similar in price, performance and engine size, the diesel Alfa leads as expected with a healthy chunk of additional torque, the Macan with a commensurate power advantage. But before we put theory into practice, a thought or two about what’s actually being fought over here. The first thing to say is that were it not for the fallout from Dieselgate, I have no doubt at all Porsche would still be selling not only diesel Macans, but Cayennes and Panameras too. Of course they would: if your car is large and heavy, diesel offers a suite of advantages over petrol many would regard as insuperable.
Most obviously they are more efficient, meaning they use less fuel – approximately 20% less or so, it is said, but my experience of big diesel burners is that their advantage over equivalent petrol cars can be greater still. In the case of these two and according to the latest WLTP measurements, the Alfa will return more than 40mpg, the Porsche less than 30mpg.
And whatever you save in fuel, you also save in CO2. If you look at tailpipe CO2 emissions, you can see that they fall year after year until the moment people got spooked by Dieselgate. And they’ve been rising ever since. Coincidence? I think not. But there’s far more to it than that: I’d have the diesel Stelvio’s torque over the petrol Macan’s power because with heavy cars – and the Macan is properly heavy – torque is more useful. Peak power can only be developed once in the entire rev range, peak torque can be maintained from little more than idle to little less than peak power. And as it is torque that you feel when you accelerate, it would be hard to overstate its importance.
Now consider that not only is the Stelvio more torquey than the Macan, it’s more than 200kg lighter too, so its crucial torque-to-weight ratio (probably the most important real-world determinant of performance potential despite the fact that hardly anyone uses it) is 209lb ft per tonne. The Macan? Just 146lb ft per tonne, a difference of more than 30%. And finally there’s range: the Stelvio has the potential to do more than 470 miles between fills even with its frankly pathetic 52-litre fuel tank. The Macan will take on board 65 litres of unleaded, but it will be a brave person who tries to stretch even that much fuel over 400 miles. Had the Stelvio the same-sized tank, it would get close to 600 miles.